JPH08208208A - Recovery of hydrazine - Google Patents

Abstract

PURPOSE: To improve hydrazine recovery efficiency by adding an alkali metal hydroxide to a hydrazine-contg. aqueous solution followed by addition of a ketone to convert the hydrazine into a ketazine which is, in turn, distilled. CONSTITUTION: An aqueous solution of an alkali metal hydroxide such as NaOH is first added to an aqueous solution containing hydrazine and ammonia or an ammonium salt at low concentrations to adjust the pH value of the system to >=10 (esp. pH11-13). Secondly, a 3-6C ketone such as methyl ethyl ketone in an amount of ca. 4 (esp. ca. 6-12) molar times of in terms of the total ketone including bound ketone based on the whole hydrazine including those bound in the form of ketazine and hydrazone is added to the system to carry out a reaction to convert the ketone into the ketazine corresponding to the hydrazine. Next, the resultant system is charged into a distillation column to conduct distillation at normal pressures, and the ammonia is recovered as a gas, and a distillate containing the ketazine is obtained. The distillate is then subjected to pressurized distillation or acid hydrolysis to recover the hydrazine in high yield, or reused as a process liquor in a hydrazine production plant by ketazine method.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for selectively recovering hydrazine from a low-concentration hydrazine-containing aqueous solution obtained in a hydrated hydrazine production plant or the like.

[0002]

2. Description of the Related Art As a method for producing hydrated hydrazine, a method of oxidizing an aqueous ammonia solution with hypochlorite, or a method of oxidizing ammonia with hydrogen peroxide in the presence of a ketone to synthesize ketazine, and hydrolyzing this ketazine There is a way to disassemble. In these manufacturing processes, a low-concentration hydrazine aqueous solution is produced or by-produced. However, since hydrazine serves as a COD source for waste water, it is necessary to perform some treatment to discard the aqueous solution containing hydrazine. Moreover, this hydrazine aqueous solution often contains inorganic ions and organic substances in addition to hydrazine.

In order to recover a hydrazine component from a low-concentration hydrazine aqueous solution, it is difficult to recover only hydrazine by simply distilling, because the vapor pressures of hydrazine and water are close to each other. Further, in the method of producing a hydrazine salt insoluble with sulfuric acid or the like, a solid separation operation is required, which is difficult to carry out industrially.

[0004]

The present invention has been made to solve the above-mentioned problems, and the purpose thereof is to more efficiently recover hydrazine from an aqueous solution containing a low concentration of hydrazine. To provide a method.

[0005]

[Means for Solving the Problems] The present inventors have conducted extensive studies to solve the above problems and completed the present invention. That is, the present invention, when a ketone is added to an aqueous solution containing a low concentration of hydrazine to convert hydrazine into a corresponding ketazine and distilling off the ketazine, an alkali metal hydroxide is added to the aqueous solution to give hydrazine. Is a method for recovering hydrazine, which is characterized by increasing the recovery rate of hydrazine.

The aqueous solution containing hydrazine, which is the object of the present invention, is not limited, but a low-concentration hydrazine aqueous solution having a hydrated hydrazine concentration of 3% or less is preferable. The reason is that it is difficult to recover hydrazine from an aqueous solution containing a low concentration of hydrazine, but according to the present invention, hydrazine can be efficiently recovered. Aqueous solution containing hydrazine to be used, ketones derived from hydrazine manufacturing process, ketazine, organic substances such as hydrazone and ammonia, inorganic substances such as ammonium ions may coexist, and coexisting ammonium ions are anions of organic acids and inorganic acids. May be combined with.

The ketone used in the present invention is preferably a ketone having a total carbon number of 3 to 6, and particularly preferably acetone and methyl ethyl ketone. Also, these ketones may be used in combination. The ketone used may contain components other than the ketone, such as water and ketazine.

The amount of the ketone added is such that the sum of the total ketone content in the hydrazine-containing aqueous solution and the added ketone is at least 4 times the molar amount of the total hydrazine content in the hydrazine-containing aqueous solution, preferably The amount is 6 to 12 times the molar amount. However, the total hydrazine content referred to here is the total amount of hydrazine bound to ketones as ketazine and hydrazone in addition to hydrated hydrazine, and the total amount of hydrazine bound to hydrazine as ketazine and hydrazone other than ketones. Means the total amount of ketones in the product.

The ketone is added to the aqueous solution containing hydrazine in advance and fed to the distillation column, or the aqueous solution containing hydrazine is fed to the distillation column in parallel with the feeding. In the latter case,
The feed stage of the ketone is preferably the same as the feed stage of the aqueous solution containing hydrazine, or a stage between the feed stage of the aqueous solution containing hydrazine and the column bottom.

Examples of the alkali metal hydroxide used in the present invention include sodium hydroxide and potassium hydroxide. Further, the form of the alkali metal hydroxide is preferably an aqueous solution from the viewpoint of easy operation.

The amount of alkali metal hydroxide added is
The amount of the hydrazine aqueous solution used is alkaline, preferably pH 10 or higher, more preferably pH 11 to 13. However, if the addition amount of the alkali metal hydroxide is too large, the load of treatment of the alkali metal hydroxide remaining in the distillation column bottoms increases.

The alkali metal hydroxide is added by adding it to an aqueous solution containing hydrazine in advance and feeding it to the distillation column, or by feeding it to the distillation column in parallel with the feeding of the aqueous solution containing hydrazine. Be seen. In the latter case, the ketone feed stage is preferably the same as the feed stage of the aqueous solution containing hydrazine, or the stage between the feed stage of the aqueous solution containing hydrazine and the top of the column. The distillation conditions may be either under reduced pressure or under increased pressure, but considering the complexity of the apparatus and the complexity of operation, it is most economical and preferable to perform under normal pressure. Further, not only continuous distillation but also batch distillation is possible. As a material for the distillation column and the reboiler, stainless steel such as SUS304, titanium, etc. can be preferably used.

In the present invention, when an aqueous solution containing hydrazine also containing ammonia or an ammonium salt is used, not only the recovery rate of hydrazine but also the recovery rate of ammonia can be increased. When the aqueous hydrazine solution contains a salt of an acid anion and an ammonium ion, the acid anion is present in the distillation bottom liquid due to the affinity between the acid anion and the added sodium ion, and the ammonium ion is used as a gas or solution of ammonia. It is possible to recover.

The distillate obtained in the present invention may contain ammonia, water, a ketone, ketazine and the like, and in addition to the distillate, ammonia can be recovered as a gas. Further, by distilling the distillate under appropriate conditions, ammonia and other components can be separated and recovered. Furthermore, hydrazine can be recovered by subjecting the distillate to pressure distillation or hydrolysis with an acid. Since the distillate contains not only ketones but also hydrazine components in the form of ketazine, it should be returned to the process liquid of the ketazine manufacturing process of the ketazine method hydrazine manufacturing plant as it is, or after separating or distilling and purifying the aqueous phase as necessary. You can also

[0015]

EXAMPLES The present invention will now be specifically described with reference to examples, but the present invention is not limited to these examples. In the Examples and Comparative Examples, the total hydrazine concentration is the total molar amount of hydrazine in the aqueous solution containing hydrazine, and the total molar amount of hydrated hydrazine and hydrazine bound to ketone as ketazine or hydrazone. Refers to the equivalent amount of hydrazine hydrate.

Example 1 An aqueous solution containing 0.5% by weight of hydrazine hydrate and 2.0% by weight of ammonia was added at a rate of 5575 g / h, and an aqueous solution of 50% by weight sodium hydroxide was added at a rate of 200 g / h.
Methyl ethyl ketone at a rate of 563 g / h at an inner diameter of 27
mm, 20-stage Oldershaw type distillation column was fed from the top to the third stage and distilled under normal pressure. Each feed solution was mixed in a line before entering the distillation column.

Of the condensate at the top of the column, 650 g / h was returned as a reflux liquid to the top of the column to obtain 968 g / h as a distillate. Ammonia was mainly recovered as a gas. The total hydrazine concentration in the bottom product was 0.05% by weight, and the amount of ammonia was 0.02% by weight. The total hydrazine content recovery rate was 91%, and the ammonia recovery rate was 99%.

Comparative Example 1 Using the same apparatus as in Example 1, 0.5 hydrazine hydrate was added.
5% by weight of an aqueous solution containing 2.0% by weight of ammonia.
563 g of methyl ethyl ketone at a rate of 575 g / h
Distillation was carried out under the same conditions as in Example 1 except that the aqueous solution of sodium hydroxide was not fed. Of the condensate at the top of the column, 650 g / h was returned as a reflux liquid to the top of the column to obtain 968 g / h as a distillate. Ammonia was mainly recovered as a gas. The total hydrazine concentration in the bottom liquor was 0.08% by weight, and ammonia was 0.1%.
It was 04% by weight. Recovery rate of total hydrazine is 85%
Met.

Example 2 Ketazine was synthesized by reacting methyl ethyl ketone, ammonia and hydrogen peroxide in the presence of a working aqueous solution containing a catalyst, and the synthesized ketazine layer was separated by liquid, and then the working aqueous solution was concentrated. A distillate containing a total hydrazine concentration of 2.3 wt%, ammonia of 6.0 wt%, reaction by-product organic matter of 12.5 wt%, and nitrate ions derived from carbonate ions and stabilizers was obtained. The distillate was mixed at a rate of 3859 g / h with a 10 wt% sodium hydroxide aqueous solution at a rate of 55 g / h, and both were mixed in advance just before entering the distillation column.
The same distillation apparatus as in Example 1 was fed from the top of the column to the third stage, and at the same time, methyl ethyl ketone was fed at a rate of 950 g / h from the top of the column to the seventh stage, and distilled under normal pressure.

Of the condensate at the top of the column, 593 g / h was returned as a reflux liquid to the top of the column to obtain 678 g / h as a distillate. Ammonia was mainly recovered as a gas. The total hydrazine concentration in the bottom product was 0.06% by weight, and the amount of ammonia was 0.04% by weight. Total hydrazine content recovery rate is 9
It was 7% and the ammonia recovery rate was 99%. The pH of the mixed liquid of the fed aqueous solution containing hydrazine and the aqueous sodium hydroxide solution at the distillation column inlet was 11.6.

Comparative Example 2 Distillation was carried out under the same conditions as in Example 2 except that the same distillate as in Example 2 was used and no aqueous sodium hydroxide solution was fed. Of the condensate at the top of the column, 593 g / h was returned as a reflux liquid to the top of the column to obtain 678 g / h as a distillate.
Ammonia was mainly recovered as a gas. The total hydrazine concentration in the bottoms was 0.11% by weight, and the amount of ammonia was 0.10% by weight. Total hydrazine content recovery rate is 95
%Met. The pH of the fed aqueous solution containing hydrazine was 9.7.

[0022]

According to the present invention, the hydrazine component can be efficiently recovered from the aqueous solution containing hydrazine. The recovered distillate containing hydrazine can be reused as a process liquid of a ketazine hydrazine production plant.

Claims (2)

[Claims] 1. When a ketone is added to an aqueous solution containing hydrazine to convert the hydrazine into a corresponding ketazine to distill and distill the ketazine, an alkali metal hydroxide is added to the aqueous solution containing hydrazine. Characteristic hydrazine recovery method. 2. The method for recovering hydrazine according to claim 1, wherein the aqueous solution containing hydrazine also contains ammonia or an ammonium salt.